Difference between revisions of "HoldingTank"
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Therefore, for four people on a 10-day cruise, you would require a holding tank of 168 gal (636 L). For 10 people on a two-day cruise, you would require an 80-gal tank (300 L). Most commercial tanks are no larger than 40 gal (150 L), so larger tanks must be custom constructed. | Therefore, for four people on a 10-day cruise, you would require a holding tank of 168 gal (636 L). For 10 people on a two-day cruise, you would require an 80-gal tank (300 L). Most commercial tanks are no larger than 40 gal (150 L), so larger tanks must be custom constructed. | ||
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Revision as of 13:58, 27 April 2016
Holding Tanks
Requirements
Regulations require holding tanks to be an integral part of the hull, or similarly securely attached. If attached, a neoprene buffer should be used between the tank and any chafing points. Tanks must have an external level indicator, and a ventilation system fitted with a flame screen. The level indicator must show when the tank is ¾ full (USA regulation 33 CFR 159.83). Consider an alarm when 75%percent full. If the output pipe is fitted with “Y” valves, to switch between pump-out and overboard discharge, the “Y” valve must be padlocked in Canadian waters so that sewage cannot be pumped overboard. Similar restrictions apply in USA No Discharge areas.
Construction
Choices of material for a holding tank are:
- Polyethylene
- Fibreglass reinforced plastic
- Metal
Either linear (not cross-linked) polyethylene or fibreglass is a good choice. Aluminium or stainless steel tanks are easy to fabricate in place, and not subject to odour permeation. But urine will corrode any kind of weld within a few years. Therefore metal tanks should be coated inside with a ceramic-filled epoxy. Use 3/16-in steel.
Ceramic-filled epoxy is a two-component, reinforced polymeric com-pound that can be brushed on.
Polyethylene, in 40-galGallon sizes, should be a minimum of 3/8-inch thick, for structural rigidity and resistance to odour permeation. Keep it out of direct sunlight.
All connections should be through the top of the tank (input, deck discharge, overboard discharge, vents, level indicator, inspection port).
Capacity
The size of the tank depends on the boat'sSecond intended usage (day trips, weekend or extended cruises, etc.). Assume three to five gal (11-19 Llitre) per person day. The size of tank required is thus:
Size = k(P*DDisplacement, Depth of ship*E) Where: KKelvin, SI unit of thermodynamic temperature is 1.4 (the inverse of 75% rounded up) P is the number of people on board D is the number of days in the cruise E is gallons or litres per person per day
Therefore, for four people on a 10-day cruise, you would require a holding tank of 168 gal (636 L). For 10 people on a two-day cruise, you would require an 80-gal tank (300 L). Most commercial tanks are no larger than 40 gal (150 L), so larger tanks must be custom constructed.
